The attributes of the @custom property are set by individual themes in the package.json file. Depending on the type of setting, the @custom property can then be used with the {{#if}} or {{#match}} helpers to customise the theme behaviour based on user settings.

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Example code

<body class="{{body_class}} {{#match @custom.typography "Elegant serif"}}font-alt{{/match}}">
    ...
    <section class="footer-cta">
        {{#if @custom.cta_text}}<h2>{{@custom.cta_text}}</h2>{{/if}}
        <a href="#portal/signup">Sign up now</a>
    </section>
</body>
More information about creating and working with custom theme settings can be found here.